Method and system for fuel vapor control

Abstract

A method and system for fuel vapor control in a hybrid vehicle (HEV). The HEV fuel vapor recovery system includes a fuel tank isolation valve, which is normally closed to isolate storage of refueling from storage of diurnal vapors. The method for fuel vapor control includes selectively actuating the fuel tank isolation valve during interrelated routines for refueling, fuel vapor purging, and emission system leak detection diagnostics to improve regulation of pressure and vacuum the HEV fuel vapor recovery system.

Description

FIELD[0001]The present application relates to fuel vapor purging in a hybrid vehicle.BACKGROUND AND SUMMARY[0002]Hybrid vehicles, such as plug-in hybrid vehicles, may have two modes of operation: an engine-off mode and an engine-on mode. While in the engine-off mode, power to operate the vehicle may be supplied by stored electrical energy. While in the engine-on mode, the vehicle may operate using engine power. By switching between electrical and engine power sources, engine operation times may be reduced, thereby reducing overall carbon emissions from the vehicle. However, shorter engine operation times may lead to insufficient purging of fuel vapors from the vehicle's emission control system. Additionally, refueling and emission control system leak detection operations that are dependent on pressures and vacuums generated during engine operation may also be affected by the shorter engine operation times in hybrid vehicles.[0003]Various strategies have been developed to address fue...

AI Technical Summary

Benefits of technology

[0002]Hybrid vehicles, such as plug-in hybrid vehicles, may have two modes of operation: an engine-off mode and an engine-on mode. While in the engine-off mode, power to operate the vehicle may be supplied by stored electrical energy. While in the engine-on mode, the vehicle may operate using engine power. By switching between electrical and engine power sources, engine operation times may be reduced, thereby reducing overall carbon emissions from the vehicle. However, shorter engine operation times may lead to insufficient purging of fuel vapors from the vehicle's emission control system. Additionally, refueling and emission control system leak detection operations that are dependent on pressures and vacuums generated during engine operation may also be affected by the shorter engine operation times in hybrid vehicles.

[0010]In such an approach, operation of the FTIV may be tightly regulated during purging to maintain a pressure in the carbon canister that is below the first threshold for purging and prevent flooding of the engine during a purging operation. Additionally, regulated bleeding of fuel vapors from the fuel tank may partially curb the high pressure fluctuations experienced in the fuel tank. Further, the present approach may allow fuel tank and canister pressures to equilibrate faster. As such, fuel tank refueling may be unsafe when fuel tank pressures are high. Thus, by equilibrating fuel tank and canister pressures faster, purging may be better coordinated with refueling operations, for example, by reducing a delay time between receiving a refueling request event and opening of a fuel tank door, after fuel tank pressure dissipation, to receive fuel.

Problems solved by technology

However, shorter engine operation times may lead to insufficient purging of fuel vapors from the vehicle's emission control system.

Additionally, refueling and emission control system leak detection operations that are dependent on pressures and vacuums generated during engine operation may also be affected by the shorter engine operation times in hybrid vehicles.

However, the inventors herein have recognized potential issues with this approach.

As one example, under conditions where the average fuel tank pressure is very high, such as in hybrid vehicle fuel systems, the pressure valve may open more frequently, or for longer durations, leading to more frequent engine air-fuel ratio fluctuations.

As a result, controlled release of fuel vapors from the fuel tank, to dissipate the fuel tank pressure, while the canister purge valve is open may be difficult to achieve, and flooding of the engine with excessive vapors may occur.

Such flooding may lead to engine stumbles and stalls, and degrade engine performance.

As such, fuel tank refueling may be unsafe when fuel tank pressures are high.

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